There is nothing worse than realizing that people are ignoring you consciously.
It raises your blood pressure like nothing else. Your rage screams in your ears, demanding to be vented. You (cleverly) walk away, thinking that a short walk around the block or through the building hoping that the action and time will wear it away.
Your fingers strike the keyboard with a particular pressure and snap as you type out the angry e-mail, ranting about the situation and trying to find anyway possible to bring the othe person down with you, any crack in their armor where you can make them feel as ignored as you. Followed, of course, by hitting the "Delete" key all the way back to the beginning of the message.
Yes, it's being ignored that is angering - but also the sense that trying to do the best thing for others is not realized at best, or simply blown off as not important as worst.
Which leaves two choices: change the perception or change the situation.
Or barring that, change the location...